This invention relates generally to chemical analysis and more particularly to a device and technique for flow injection analysis.
In a known device for flow injection analysis, a peristaltic pump is provided with parallel delivery in two hose conduits. In one of these hose conduits a reagent is delivered. A sample liquid is taken in through the other hose conduit which is connected to an intake tube which dips into a sample vessel. The sample vessels are arranged on an turntable. Thereby the different samples arranged in the sample vessels are taken in consecutively. The reagent hose conduit communicates with a relatively long conduit which leads through a photometer vessel to a waste vessel. A loop of tubing can be inserted between the intake tube and the peristaltic pump and can be optionally inserted by a changeover valve in the reagent flow between the reagent hose conduit and the reagent flow path to the photometer vessel, i.e., to measuring apparatus. Then a continuous flow of reagent flows through the conduit and to the photometer vessel. A definite volume of sample liquid is supplied, i.e., "injected", into this flow of reagent through the changeover valve. On the way to the photometer vessel in the relatively long conduit, the sample liquid has the opportunity to mix up and react with reagent. The change of color occurring thereby is measured. Such an arrangement for flow injection analysis offers an advantage in that it is quite easy to automate. In the described device the reagent serves at the same time as carrier liquid which rinses the sample liquid out of the tube circuit.
In another known device of the present type, the peristaltic pump delivers into three hose conduits at the same time. A first hose conduit is connected to a reagent reservoir and carries a flow of reagent as in the previously described device. A second hose conduit is connected to an intake tube which is arranged to take in sample liquid from sample vessels which are located on a turntable. A third hose conduit delivers air, such that the different samples are separated by air bubbles. The separation of the samples by air bubbles is effected upstream of the point at which reagent is injected into the sample liquid flow.
Hose pumps comprise a rotating carrier on which rollers are mounted in a regular arrangement about the rotational axis. A flexible hose is guided along a curved surface extending through an angular range about the rotational axis. The rollers contact the hose and compress it. Thereby, in one position of the carrier, a section or a chamber of the hose is closed towards the inlet-side and towards the outlet side. With further rotation of the carrier, the roller on the outlet side lifts off the curved surface to establish communication with the outlet. The liquid volume enclosed in the chamber is pressed out to the outlet by the roller on the inlet side. This roller on the inlet side of the section just mentioned simultaneously forms the roller on the outlet side of a following chamber. This chamber is enlarged when the last mentioned roller is moved along the hose by the carrier. Liquid is aspirated into the chamber until the following chamber is again closed towards the inlet by a further roller provided on the carrier. Then the described operation is repeated.
Usually such peristaltic pumps are driven by a conventional electric motor running at a constant rotary speed. The carrier rotates at a constant angular speed but the delivery of the peristaltic pump becomes nonuniform, i.e., when the rollers lift off the hose, the delivery decreases. The delivery of the peristaltic pump can also vary because of ageing of the hose, temperature variations and similar disturbances.
It is known to increase the rotational speed of the carrier when the rollers lift off to counteract this geometrically caused decrease of the delivery. A complex mechanical transmission is utilized to so increase the rotational speed which represents a very expensive solution.
Also, in devices of the present type, it is important to mix up liquids in exactly defined ratios and such non-uniformities of the delivery may cause measuring errors.
There are commercial sample inlet devices in which the sample liquid is passed through a changeover valve in a loop of tubing. Then this loop of tubing is connected to a carrier liquid flow path by means of a changeover valve. Then the loop of tubing is rinsed by the carrier liquid and the sample liquid is taken along by the carrier liquid. The changeover valve is reversed by a driving motor and for that purpose, the driving motor has to apply a relatively strong torque. The driving motor switches the changeover valve over from one switching position to another switching position between two stops. Known sample inlet devices of this type provide a sliding clutch between the driving motor and the changeover valve in order to ensure that the stops and the driving motor are not damaged. Such a sliding clutch is expensive and susceptible to trouble.
It is an object of the present invention to provide a new and improved flow injection device.
Another object of the invention to provide such a device wherein the peristaltic pump provides a delivery which is constant as a function of time.
Yet another object of the invention is to provide such a device which allows more flexible control of the liquid flows.
Other objects will be in part obvious and in part pointed out more in detail hereinafter.
Accordingly, it has been found that the foregoing and related advantages are attained in flow injection analysis apparatus having a measuring apparatus for measuring a looked-for element in an atomic state, a reagent conduit for conducting a flow of reagent to the measuring apparatus, and a sample injection apparatus for injecting a predetermined volume of sample liquid into the flow of reagent in the reagent conduit at a point upstream of the measuring apparatus. A peristaltic pump generates the flow of reagent and has a pump motor configured to be advanced stepwise in pumping the reagent. An electronic control controls the stepwise advancement of the pump motor to produce constant delivery through the reagent conduit. Preferably, the pump motor is a stepper motor and is controlled in a nonuniform step sequence to compensate the geometrically caused nonuniformity of delivery of the peristaltic pump, i.e, the nonuniformities of the delivery of the peristaltic pump caused by geometry are compensated by inverse nonuniformities of the angular rates. In an alternate configuration, a stepper motor is utilized to drive the changeover valve for alternately interconnecting a loop of tubing from the sample flow path to the carrier liquid path for injection into the reagent conduit.
Suitably the peristaltic pump motor is a stepper motor. Alternately, a normal electric motor could be used in which certain positions are predetermined, e.g., by means of an aperture disc and a photoelectric barrier, with a change over from one of these positions to the next being effected by suitable circuitry.
The motor which is arranged to be advanced stepwise allows an easy adaptation to the required modes of operation by program-controlled electronic control and to the uniformity of the delivery as well as with respect to the delivery flow and the taking into account of corrections.
One possibility of using a motor which is arranged to be advanced stepwise is that the step sequence of the motor is controlled non-uniformly by electronic control such that a constant delivery of the peristaltic pump is attained.
It is also advantageous when predetermined positions of the peristaltic pump can be detected by position detectors which provide position signals. These position signals may be supplied to the control electronics for synchronizing the non-uniformity of the step sequence with the delivery non-uniformity of the peristaltic pump caused by geometric conditions.
Another advantageous configuration is that the speed of the motor which is arranged to be advanced stepwise is controllable by an output signal of the measuring apparatus.
Another aspect of the invention is that the sample inlet device comprises a loop of tubing which is arranged to be connected optionally to the sample liquid flow path or to the conduit for the carrier liquid and that the changeover valve is arranged to be driven by a motor arranged to be advanced stepwise and is directly coupled thereto. In this way the necessity of a sliding clutch is avoided which according to prior art as described above involves high expenditure and is susceptible to trouble. Also, by such a motor, the changeover valve may be positioned gently in a definite valve position and stops are not necessary. Controlling is also effected by a program. Stops can be omitted. Furthermore, there is the possibility that the changeover valve is movable into more than two valve positions by the motor which is arranged to be advanced stepwise.